This invention relates to monolithic refractory compositions. More specifically, the invention relates to silica-doped, chrome-alumina plastics and ramming mixes.
Specialty refractories, such as refractory plastics and ramming mixes cure to form monolithic, integral structures after application. Such plastics and ramming mixes are mixes of refractory grains and plastic clays or plasticizers from which a plastic mixture is formed by adding water. The differences between ramming mixes and refractory plastics are slight. Generally, such plastics have a higher plasticity than ramming mixes and can be installed without forms, whereas ramming mixes are installed behind forms. Thus, both mixtures can be used either to repair irregularly worn furnace lining or to form monolithic furnace walls in new installations.
In the past, workers in the art have utilized a number of chrome-alumina specialty products. These chrome-alumina specialties, which utilize high purity Cr.sub.2 O.sub.3 and tabular alumina in conjunction with a phosphate biner and low levels of clay, provide high refractoriness and very good resistance to both acid and basic slags.
There is a need, however, to increase the strength of these refractories in the intermediate temperature range of 2,300.degree. F. to 2,800.degree. F. Below 2,300.degree. F., the phosphate bond in these refractories provides adequate strength, whereas above 2,800.degree. F., the Cr.sub.2 O.sub.3 -Al.sub.2 O.sub.3 solid solution is sufficiently developed to provide sufficient strength. In the temperature range of 2,300.degree. F. to 2,800.degree. F., however, which is involved in a significant number of iron and steel making processes, the phosphate bond in these refractories appears to be partially lost and the Cr.sub.2 O.sub.3 -Al.sub.2 O.sub.3 solid solution is not well developed.
Accordingly, workers in the art have sought improved chrome-alumina plastics and ramming mixes which, while retaining high refractoriness and good resistance to both acid and basic slags, also possess increased strength in the temperature range of 2,300.degree.-2,800.degree. F. The refractory compositions of the present invention, having good hot strength in the 2,300.degree.-2,800.degree. F. temperature range, as well as slag erosion resistance and resistance to iron oxide penetration, represent an important contribution to the art.